As a typical example of a conventional liquid ejecting apparatus, there is an ink jet recording apparatus having an ink jet recording head for image recording. As other liquid ejecting apparatuses, for example, an apparatus having a coloring material ejecting head used to manufacture color filters such as a liquid crystal display, an apparatus having an electrode material (conductive paste) ejecting head used to form electrodes such as an organic EL display and a face emission display, an apparatus having a biological organic substance ejecting head used to manufacture biological chips, and an apparatus having a sample ejecting head as a precise pipette may be cited.
In the ink jet recording apparatus which is a typical example of the liquid ejecting apparatus, an ink jet recording head having a pressure generation means for pressurizing a pressure generation chamber and a nozzle opening for jetting pressurized ink as ink drops is loaded in a carriage.
In the ink jet recording apparatus, ink in an ink container is continuously fed to a recording head via a flow path, thus printing can be continued. The ink container is formed as a removable cartridge which can be exchanged by a user, for example, at the point of time when ink is consumed.
Conventionally, as a method for controlling ink consumption in the ink cartridge, there are a control method for totalizing the number of jets of ink drops by the recording head and the ink amount sucked in by maintenance by the software, thereby calculating the ink consumption and a method for controlling ink at the point of time when a predetermined amount of ink is actually consumed by an electrode for liquid level detection which is attached to the ink cartridge.
However, the method for totalizing the jet count and ink amount of ink drops by the software and calculating the ink consumption has a problem as indicated below. Some heads have variations in weight in jetted ink drops. Although weight variations of ink drops do not affect the image quality, in consideration of cumulative errors of the ink consumption due to variations, an amount of ink given a margin is filled in the ink cartridge. Therefore, a problem arises that in some individual, the margin of ink may be left over.
On the other hand, the method for controlling the point of time of ink consumption by the electrode can detect the actual amount of ink, so that the ink residue can be controlled highly reliably. However, the detection of the ink level depends on the conductivity of ink, so that there are defects that the kind of detectable ink is limited and the seal structure of the electrode is complicated. Further, as a material of the electrode, a noble metal which is conductive and corrosion resistant is generally used, so that the manufacturing cost of ink cartridges is increased. Furthermore, two electrodes must be mounted, so that the manufacturing steps are increased and as a result, the manufacturing cost is increased.
The apparatus developed to solve the aforementioned problems is disclosed as a piezoelectric device in Japanese Patent Application 2001-146024. This piezoelectric device can accurately detect the liquid residue and requires no complicated seal structure, so that it can be mounted and used in a liquid container.
Namely, according to the piezoelectric device described in Japanese Patent Application 2001-146024, using that the resonance frequency of a residual vibration signal generated due to a residual vibration (a free vibration) of the vibration part of the piezoelectric device forcibly vibrated by a driving pulse is changed between a case that there is ink in the space opposite to the vibration part of the piezoelectric device and a case that there is no ink (or little ink), the ink residue in the ink cartridge can be monitored.
FIGS. 24A, 24B, and 24C show an actuator constituting the aforementioned piezoelectric device. An actuator 106 has a substrate 178 having a circular opening 161 at almost the center thereof, a vibration plate 176 arranged on one surface (hereinafter, referred to as the surface) of the substrate 178 so as to cover the opening 161, a piezoelectric layer 160 arranged on the side of the surface of the vibration plate 176, an upper electrode 164 and a lower electrode 166 holding the piezoelectric layer 160 on both sides thereof, an upper electrode terminal 168 electrically joining to the upper electrode 164, a lower electrode terminal 170 electrically joining to the lower electrode 166, and an auxiliary electrode 172 arranged between the upper electrode 164 and the upper electrode terminal 168 for electrically joining the two.
The piezoelectric layer 160, the upper electrode 164, and the lower electrode 166 respectively have a circular part which is a main portion thereof. And, the respective circular parts of the piezoelectric layer 160, the upper electrode 164, and the lower electrode 166 form piezoelectric elements.
The vibration plate 176 is formed on the surface of the substrate 178 so as to cover the opening 161. A cavity 162 is formed by the part of the vibration plate 176 opposite to the opening 161 and the opening 161 of the substrate (the cavity forming member) 178. The surface (hereinafter, referred to as the rear) of the substrate 178 on the opposite side of the piezoelectric device faces on the inside of the ink container. Therefore, the cavity 162 is formed so as to make contact with a liquid (ink). Further, even if a liquid enters inside the cavity 162, to prevent it from leaking on the surface side of the substrate 178, the vibration plate 176 is attached liquid-tightly to the substrate 178.
The lower electrode 166 is positioned on the surface of the vibration plate 176. The center of the circular part which is the main portion of the lower electrode 166 and the center of the opening 161 are attached so as to coincide with each other. Further, on the surface side of the lower electrode 166, the piezoelectric layer 160 is arranged and formed so that the center of the circular part coincides with the center of the opening 161.
And, in the actuator (piezoelectric device) 106 by the related art, the size (area) of the circular part of the lower electrode 166 is preset so as to be smaller than the size (area) of the opening 161, and the overall circular part of the lower electrode 166 is arranged within the area corresponding to the opening 161. Further, the area of the circular part of the piezoelectric layer 160 is preset so as to be smaller than the area of the opening 161 and larger than the area of the circular part of the lower electrode 166.
On the surface side of the piezoelectric layer 160, the upper electrode 164 is arranged and formed so that the center of the circular part which is the main portion thereof coincides with the center of the opening 161. The area of the circular part of the upper electrode 164 is preset so as to be smaller than the areas of the opening 161 and of the circular part of the piezoelectric layer 160 and so as to be larger than the area of the circular part of the lower electrode 166.
Therefore, the main portion of the piezoelectric layer 160 is structured so as to be held by the main portion of the upper electrode 164 and the main portion of the lower electrode 166 respectively on the surface side and rear side thereof. The circular parts of the upper electrode 164 and the lower electrode 166 which are respectively the main portions form the piezoelectric element of the actuator 106. The piezoelectric element is in contact with the vibration plate 176.
By use of such a structure, the vibration area of the vibration plate 176 which vibrates actually is decided by the opening 161. Further, among the circular part of the lower electrode 166 and the circular part of the upper electrode 164 which are electrically connected to the piezoelectric layer 160, the circular part of the lower part 166 is smaller, so that the circular part of the lower electrode 166 decides a part of the piezoelectric layer 160 producing the piezoelectric effect.
As described above, in the actuator 106 (piezoelectric device) by the related art, among the circular main portion of the upper electrode 164, the circular main portion of the piezoelectric layer 160, the circular main portion of the lower electrode 166, and the circular opening 161, the opening 161 has the largest area, and the main portion of the piezoelectric player 160 has the next largest area, and the main portion of the upper electrode 164 has the next largest area, and the main portion of the lower electrode 166 has the smallest area.
And, in the aforementioned actuator 106 by the related art, the residual vibration (free vibration) of the vibration part generated after the driving pulse is applied to the piezoelectric element and the vibration part is forcibly vibrated is detected as counter electromotive force by the same piezoelectric element. And, using that the residual vibration state of the vibration part is changed before and after the liquid level in the ink container passes the installation position (strictly speaking, the position of the cavity 162) of the actuator 106, the residual ink amount in the ink container can be detected.
However, in the aforementioned conventional liquid-detecting device (piezoelectric device), there are problems imposed as mentioned below.
Firstly, the output of the counter electromotive force generated in the piezoelectric element by the residual vibration of the vibration part of the liquid-detecting device is small, so that it is difficult to detect the counter electromotive force. The reason seems to be that the deformed shape (the deformation mode) of the vibration part when the driving pulse is applied to the piezoelectric element and the vibration part is forcibly vibrated and the deformed shape (the deformation mode) of the vibration part at the time of free vibration after forcible deformation are greatly different from each other.
Secondly, a problem arises that during free vibration of the vibration part after forcible deformation, other than the vibration frequency necessary as a detection object, an unnecessary high order of vibration mode is excited. Particularly, when the lower electrode is displaced in the vibration part due to manufacture variations, an unnecessary vibration is increased and the vibration frequency may not be detected or may not be detected correctly.
Further, as shown in FIGS. 24A, 24B, and 24C, in the conventional liquid-detecting device (piezoelectric device), a part of the hard and fragile piezoelectric film 160 is extended toward the upper electrode terminal 168 so as to cross the periphery of the cavity 162. Therefore, a problem arises that the piezoelectric film 160 may be cracked at a position corresponding to the periphery of the cavity 162.